A growing body of evidence suggests that an individual's social network may be an important determinant of health and well-being -- for example, socially isolated individuals appear to be at greater risk for all causes of premature mortality, including mortality from cardiovascular disease. Preliminary evidence implicates excessive cardiovascular reactivity to psychological challenge as a potential risk factor for coronary artery disease and hypertension, and human and animal studies suggest that excessive reactivity may have some important psychosocial correlates. The overall objective of the proposed project is to further investigate the effects of social support on cardiovascular responsivity to challenge in humans, thereby advancing our understanding of one plausible mechanism by which social relationships might alter cardiovascular health. A model is employed which emphasizes two fundamental dimensions of interpersonal functioning -- dominance vs. submissiveness (here called "evaluation") and affiliation vs. hostility (here called "affilation"). The first two studies are designed to investigate how alterations in the affiliative and evaluative dimensions of interpersonal interaction with a partner can alter the partner's influence on a subject's cardiovascular responsiveness to a laboratory challenge. The second set of two studies is designed to investigate the mechanisms by which a partner's presence may alter cardiovascular reactivity, exploring the neutralizing impact of social affiliation on the performance incentive effects associated with social threat, and associated reductions in cardiovascular response. The third set of two studies is designed to examine the generalizability of the effects of social support on reactivity, exploring the influence of these effects in males and females, in individuals with coronary-prone behavior, and within the context of a primary relationship. Together, these three studies will advance our understanding of one of the mechanisms by which social processes may alter cardiovascular disease risk.